#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int main()
{
	int i, j;
	int sum = 0;
	int mid = 0;
	for (i = 1; i <= 20; i++)
	{
		mid += 1;
		sum += 1;
		if (mid % 2 == 0)
		{
			sum += 1;
			mid = 0;
		}
	}
	printf("%d", sum);
	return 0;
}